1. Field of the Invention
The present invention relates generally to a method and apparatus for receiving data in a User Equipment (UE) in a mobile communication system and more particularly, to a Discontinuous Reception (DRX) method and apparatus of a UE in a mobile communication system.
2. Description of the Related Art
DRX is a type of packet reception scheme used at a UE in a mobile communication system. In DRX, the UE keeps a receiver on only during a data reception-expected period and turns off the receiver during a non-data reception-expected period, rather than keep the receiver on all the time.
FIG. 1 illustrates the concept of a conventional DRX operation. However, before describing FIG. 1 in specific detail, for packet reception in a DRX mode, the following terms should be defined.
(1) Active Period: The receiver of the UE is in an “on state”. If DRX is set on a service basis, the receiver expects data reception for a service during an active period of the service.
(2) Sleep Period: The receiver is in an “off state”. If DRX is set on a service basis, the receiver does not expect data reception for a service during a sleep period of the service. The sleep period is defined to save power for the UE. Because the UE does not expect to receive any data during the sleep period, it turns off its receiver, thus minimizing power consumption.
(3) DRX cycle lengths 110 and 120: The interval between one active period and the next active period with regard to data of a service.
A decision to turn off the receiver of the UE is made according to whether the sleep periods of a plurality of services provided to the UE are overlapped. For example, if service A and service B are provided to the UE and a current period is a sleep period for service A and an active period for service B, the UE should keep its receiver on. If the sleep periods of service A and service B coincide with each other, the receiver of the UE is turned off. For ease of description, the following description is made on the assumption that the UE receives one service, i.e., its receiver is on during an active period and off during a sleep period.
Referring to FIG. 1, the start position 130 or end position of an active period is determined according to the reception time or received amount of data. In general, the start position 130 of the active period is determined using a UE Identifier (ID) and a DRX cycle length.
In a conventional packet communication system, however, the DRX cycle length is always constant, as illustrated in FIG. 1. As a result, when the UE receives discontinuous data such as Web browsing service data or File Transfer Protocol (FTP) service data in this DRX mode, it consumes unnecessary power due to the nature of the discontinuous data. With reference to FIG. 2, a detailed description will be made of the problem with reception of discontinuous data in the DRX mode. For simplicity, Web browsing service data (Web data, for short) is used as discontinuous data, by way of example.
FIG. 2 illustrates a typical traffic pattern of Web data. Referring to FIG. 2, when a user transmits a message requesting a Web page, for example, a HyperText Transfer Protocol (HTTP) request to a network through his UE in step 215, it receives Web data corresponding to the request message. Reference numeral 205 denotes packets downloaded to the UE from the network (i.e., downlink packet data). A time period for which the UE expects to download the downlink packet data is referred to as a downloading phase 225. When the UE transmits a Transmission Control Protocol Acknowledgment (TCP ACK) 210 for the last downlink packet data to the network in the downloading phase 225, the downloading phase 225 is over as all of the Web data has been downloaded. Then the user starts to read the downloaded Web data through the UE. This is called a reading phase 230. In the reading phase 230, no data is transmitted and received. Notably, the downloading phase 225 and the reading phase 230 are distinguished conceptually for illustrative purposes, though not physically. In real implementation, an active period and a sleep period are physically distinguishable from each other.
If the user later requests new Web data to the network, that is, if the UE transmits a new HTTP request message in step 215, downloading of the new Web data starts in step 220.
As described above, when the user receives the Web browsing service from the network, data transmission and reception frequently take place between the UE and the network in the downloading phase 225, whereas data transmission and reception seldom occurs in the reading phase 230. However, when Web data having this feature is received in the conventional DRX scheme, active periods are disposed at the same cycle in both the downloading phase 225 and the reading phase 230. That is, the conventional DRX is characterized by applying the same DRX cycle length to the downloading phase 225 and the reading phase 230. Accordingly, despite no need for data reception in the reading phase 230, the UE keeps its receiver in an on state, thereby consuming unnecessary power.